Potential energy surface

About: Potential energy surface is a research topic. Over the lifetime, 11674 publications have been published within this topic receiving 307691 citations.

A variational method for the calculation of vibrational levels of any triatomic molecule

Abstract: Assuming that the potential energy surface is known, a variational method is presented for the determination of vibrational frequencies which is suitable for any triatomic molecule The harniltonian is expressed as a function of two bond lengths and the included angle The expansion functions are products of either Morse oscillator functions or harmonic oscillator functions for the stretching vibrations and spherical harmonics for the bending vibration Results are presented for linear, quasilinear and bent molecules

Structures for d0 ML6 and ML5 complexes

Abstract: A second-order Jahn-Teller argument is given to explain why certain d 0 ML 6 and ML 5 molecules will have geometries different from the octahedron and the trigonal bipyramid, respectively, as given by the VSEPR rules. Ab initio molecular orbital calculations were used to explore the potential energy surface for a variety of molecules. In the CrH 6 system, 20 stationary points were located and six were selected for study using a number of basis sets and electron correlation methods. The global minimum appears to be a C 3v (η 2 -H 2 ) 3 Cr isomer which QCISD(T) calculations put at being 165 kcal/mol more stable than the octahedral (On) one

Ring polymer molecular dynamics with surface hopping.

Abstract: We propose a ring polymer molecular dynamics method for the calculation of chemical rate constants that incorporates nonadiabatic effects by the surface-hopping approach. Two approximate ring polymer electronic Hamiltonians are formulated and the time-dependent Schrodinger equation for the electronic amplitudes is solved self-consistently with the ring polymer equations of motion. The beads of the ring polymer move on a single adiabatic potential energy surface at all times except for instantaneous surface hops. The probability for a hop is determined by the fewest-switches surface-hopping criterion. During a surface hop all beads switch simultaneously to the new potential energy surface with positions kept unchanged and momenta adjusted properly to conserve total energy. The approach allows the evaluation of total rate coefficients as well as electronic state-selected contributions. The method is tested against exact quantum mechanical calculations for a one-dimensional, two-state model system that mimics a prototypical nonadiabatic bimolecular chemical reaction. For this model system, the method reproduces quite accurately the tunneling contribution to the rate and the distribution of reactants between the electronic states.

An ab initio molecular orbital-valence bond (MOVB) method for simulating chemical reactions in solution

Abstract: A mixed molecular orbital and valence bond (MOVB) method for describing the potential energy surface of reactive systems has been developed and applied to a model proton transfer reaction in aqueous solution. The MOVB method is based on a block-localized wave function (BLW) approach for defining the diabatic electronic states. Then, a configuration interaction Hamiltonian is constructed using these diabatic states as the basis function. It was found that the electronic coupling energy is large with a value of about 30 kcal/mol for the H3N−H−NH3+ system, whereas the predicted activation barrier is only 1.2 kcal/mol using the 3-21G basis set. The MOVB results are found to be in good accord with the corresponding ab initio Hartree−Fock calculations for the proton transfer process. We have also incorporated solvent effects into the MOVB Hamiltonian in the spirit of combined QM/MM calculations, and have modeled the proton transfer between ammonium ion and ammonia in water using Monte Carlo simulations. The pot...

Experimental and Theoretical Examination of C−CN and C−H Bond Activations of Acetonitrile Using Zerovalent Nickel

Abstract: Experimental and density functional theory show that the reaction of acetonitrile with a zerovalent nickel bis(dialkylphosphino)ethane fragment (alkyl = methyl, isopropyl) proceeds via initial exothermic formation of an η2-nitrile complex. Three well-defined transition states have been found on the potential energy surface between the η2-nitrile complex and the activation products. The lowest energy transition state is an η3-acetonitrile complex, which connects the η2-nitrile to a higher energy η3-acetonitrile intermediate with an agostic C−H bond, while the other two lead to cleavage of either the C−H or the C−CN bonds. Gas-phase calculations show C−CN bond activation to be endothermic, which contradicts the observation of thermal C−CN activation in THF. Therefore, the effect of solvent was taken into consideration by using the polarizable continuum model (PCM), whereupon the activation of the C−CN bond was found to be exothermic. Furthermore the C−CN bond activation was found to be favored exclusively o...